1. Field of the Invention
The present invention relates to an image communication apparatus for receiving image data from an external device via a network and a method for controlling the image communication apparatus.
2. Description of the Related Art
To communicate information among remote offices, image data is transmitted and received using facsimile machines. The facsimile machines transmit and receive image data over a public switched telephone network (PSTN) using a protocol in conformance with ITU-T T.30.
In addition to using facsimile machines, recently, image data has been transmitted and received using an e-mail by attaching the facsimile-based image data to the e-mail in accordance with the protocol in conformance with ITU-T T.37. In this communication method, since data is transmitted and received via an Internet protocol (IP) network, image data can be transmitted and received at a cost lower than that required for the facsimile communication in accordance with the protocol in conformance with ITU-T T.30.
Furthermore, a real-time Internet facsimile communication (hereinafter referred to as “IP-FAX communication”) has been developed in which facsimile data is transmitted and received in real time via an IP network using an ITU-T T.38 protocol. More specifically, a facsimile machine at a transmission side is directly connected to a facsimile machine at a reception side via an IP network so that a facsimile signal in conformance with ITU-T T.30 is converted to TCP/IP packets and is transmitted and received.
In the above-described IP-FAX communication, the call control procedure based on ITU-T H.323 is employed. Recently, session initiation protocol (SIP), which is similar to ITU-T H.323 protocol, has garnered increased attention.
When comparing the call control procedure in conformance with ITU-T H.323 with SIP, ITU-T H.323 protocol is more complicated since ITU-T H.323 includes a variety of sub-protocols. In contrast, SIP defines only basic session control sub-protocols, such as sub-protocols for starting, changing, and ending a session. Accordingly, SIP is relatively simplified. Consequently, SIP is highly flexible and can be easily integrated into other systems.
SIP includes a user agent, which is a user terminal (e.g., an IP telephone), and a SIP server. The term “SIP server” collectively refers to a proxy server, a redirect server, and a registrar server. Therefore, for example, the alternative address of a facsimile machine on a reception side can be registered using the redirect server.
More specifically, in the case where a particular facsimile machine on a reception side is specified as a destination address of image data, another facsimile machine is registered with a redirect server as a forward address of the image data. Thus, when a facsimile machine on a transmission side transmits image data to the particular address, the alternative address is read out from the redirect server. Subsequently, a call connection is started so that a connection between the facsimile machine on a transmission side and a facsimile machine at the alternative address is established. The facsimile machine on a transmission side then transmits the image data to the facsimile machine at the alternative address (refer to, for example, Japanese Patent Laid-Open No. 2005-94662).
By using the functions of SIP, if an image communication apparatus on a reception side cannot receive image data due to a print paper runout state or an overload state, such as a memory full state or a session full state, an image communication apparatus on a transmission side transmits the image data to an image communication apparatus at the alternative address.
In this way, a session is established between the image communication apparatus on a transmission side and the image communication apparatus at the alternative address, which is a forward address. Thus, facsimile communication can be performed. Accordingly, the image communication apparatus on a transmission side need not wait for starting transmission for a long time. However, in such a case, the image data is transferred to an image communication apparatus that is different from the originally intended image communication apparatus for receiving the image data, although a user on a reception side registers the forward address. That is, the user of the image communication apparatus at the original destination address has to go to the image communication apparatus at the forward address in order to pick up the transmitted image data. In addition, if the image communication apparatus that received the forwarded image data stores the image data for a long time, a memory resource may be exhausted.